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Chapter 4. Bacteriophage 噬菌体 PowerPoint PPT Presentation

Chapter 4. Bacteriophage 噬菌体. Bacteriophages ( phages ) are obligate intracellular parasites that multiply inside bacteria by making use of some or all of the host biosynthetic machinery . They are viruses that infect bacteria. Bacteriophage (Phage).

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Chapter 4. Bacteriophage 噬菌体

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Bacteriophages ( phages ) are obligate intracellular parasites that multiply inside bacteria by making use of some or all of the host biosynthetic machinery . They are viruses that infect bacteria.

Bacteriophage (Phage)

Definition - Obligate intracellular parasites that multiply inside bacteria by making use of some or all of the host biosynthetic machinery

Significance

Models for animal cell viruses

Gene transfer in bacteria

Medical applications

Identification of bacteria - phage typing

Treatment and prophylaxsis???

viral common properties smallest，simple structure DNA/RNA病毒的基本特性

parasite in living cell

widespread existence 分布广泛

high host –specific parasitism严格的宿主特异性

Main contents

1 COMPOSITION AND STRUCTURE OF BACTERIOPHAGE

2 PHAGE MULTIPLICATION CYCLE

3 APPLICATION OF BACTERIOPHAGE

Requirement

Master the interrelation between phage and bacteria

Master the following concepts :

1. lysogenic state 2. lysogenic phage (temperate phage)

3.lysogenec bacteria 4.prophage

Understand the.size, shape and structure of phage.

[Class hour: 1 hours ]

Composition of Bacteriophage

nucleic acid: either DNA or RNA but not both

ds DNA, ss RNA, ss DNA

unusual or modified bases

encode 3-5 gene products

Protein: function in infection and protect the nucleic acid

Biological properties生物学性状

Shape and structure Seen by EM :icosahedral 二十面体

Tadpol蝌蚪形

microsphere微球形

slim rod丝形

head core DNA/RNA tail pipe-like

capsid protein coat base plate

Antigenicity 抗原性

Resistive 抵抗力

>Bacteria 75°C 30′

sensitive to rays

filamentous

Head/Capsid

Contractile Sheath

Tail

Tail Fibers

Base Plate

Composition and Structure

Composition

Nucleic acid

Genome size

Modified bases

Protein

Protection

Infection

Structure (T4)

Size

Head or capsid

Tail

Types of Bacteriophage

Lytic or Virulent Phages毒性噬菌体

Lytic or virulent phages are phages which can only multiply in bacteria and kill the cell by lysis at the end of the life cycle.

噬菌体的种类

毒性噬菌体（virulent phage）

能在宿主菌细胞内复制增殖，产生许多子代噬菌体，并最终裂解细菌，称为毒性噬菌体

温和噬菌体（temperate phage）/

溶原性噬菌体（lysogenic phage）

噬菌体基因与宿主菌染色体整合，不产生子代噬菌体，但噬菌体DNA能随细菌DNA复制，并随细菌的分裂而传代

Life Cycle毒性噬菌体复制周期

Adsorption吸附Penetration穿入

Biological Synthesis生物合成

Maturation and Release成熟和释放

Lysogenic or Temperate Phage溶原性噬菌体或温和噬菌体

Lysogenic or temperate phages are those that can either multiply via the lytic cycle or enter a quiescent state in the cell. In this quiescent state most of the phage genes are not transcribed; the phage genome exists in a repressed state. The phage DNA in this repressed state is called a prophagebecause it is not a phage but it has the potential to produce phage. In most cases the phage DNA actually integrates into the host chromosome and is replicated along with the host chromosome and passed on to the daughter cells. The cell harboring a prophage is termed a lysogenic bacterium.

Lytic phage are enumerated by a plaque assay. A plaque is a clear area which results from the lysis of bacteria. Each plaque arises from a single infectious phage. The infectious particle that gives rise to a plaque is called a pfu (plaque forming unit).

Lytic or Virulent Phages毒性噬菌体

Lytic or virulent phages are phages which can only multiply in bacteria and kill the cell by lysis at the end of the life cycle.

噬菌现象

液体培养基 混浊 澄清

固体培养基中，出现噬斑（plaque）

一定体积内的噬斑形成单位数目（pfu）

温和噬菌体

前噬菌体（prophage）

溶原性细菌（lysogenic bacterium）

溶原性（lysogeny）

溶原状态

溶原性周期和溶菌性周期

溶原性转换

Animation summarizing the lysogenic life cycle of a temperate bacteriophage.

Lysogenic bacterium

PHAGE MULTIPLICATION CYCLE- Life Cycle:

Lysogenic or Temperate Phage溶原性噬菌体或温和噬菌体

溶原性细菌的溶原性周期和溶菌性周期

Application of Bacteriophage噬菌体的应用

Used in treatment of bacterial infections细菌感染的诊断与治疗

Used for the identification of pathogenic bacteria细菌的鉴定与分型 (phage typing噬菌体型分型)

Used in molecular biology分子生物学研究的重要工具

Medical Applications of Phage

“I strongly believe phage could become an effective antibacterial tool” - Carl Merril, Chief of the Laboratory of Biochemical Genetics, National Institute of Mental Health, NIH.

“It might be another string on the bow, such that when (conventional antibiotics) fail, here’s something that has a chance of working. But it’s not going to be a panacea” - Joshua Lederberg, Sackler Foundation Scholar at The Rockefeller University